In the drilling and completion industry, the formation of boreholes for the purpose of production or injection of fluid is common. The boreholes are used for exploration or extraction of natural resources such as hydrocarbons, oil, gas, water, and alternatively for CO2 sequestration. A production tubing string is typically run thousands of feet into a well bore. Generally, when running a tubing string downhole, it is desirable, and in some cases required, to include a safety valve on the tubing string. The safety valve typically has a fail safe design whereby the valve will automatically close to prevent production from flowing through the tubing, should, for example, the surface production equipment be damaged or malfunction.
Should the safety valve become inoperable, the safety valve may be retrieved to surface by removing the tubing string, as described hereinafter. The tubing retrievable surface controlled subsurface safety valve (“TRSV”) is attachable to production tubing string and includes a flapper pivotally mountable on the lower end of the safety valve assembly by a flapper pin. A torsion spring is provided to bias the flapper in the closed position to prevent fluid flow through the tubing string. When fully closed the flapper seals off the inner diameter of the safety valve assembly preventing fluid flow therethrough. A flow tube is provided above the flapper to open and close the flapper. The flow tube is adapted to be movable axially within the safety valve assembly. When the flapper is closed, the flow tube is in its uppermost position; when the flow tube is in its lowermost position, the lower end of the flow tube operates to extend through and pivotally open the flapper. When the flow tube is in its lowermost position and the flapper is open, fluid communication through the safety valve assembly is allowed. A rod piston contacts the flow tube to move the flow tube. The rod piston is located in a hydraulic piston chamber within the TRSV. The upper end of the chamber is in fluid communication, via a control line, with a hydraulic fluid source and pump at the surface. Seals are provided such that when sufficient control fluid (e.g. hydraulic fluid) pressure is supplied from surface, the rod piston moves downwardly in the chamber, thus forcing the flow tube downwardly through the flapper to open the valve. When the control fluid pressure is removed, the rod piston and flow tube move upwardly allowing the biasing spring to move the flapper and thus the valve, to the closed position.
If the TRSV becomes inoperable or malfunctions due to the buildup of materials such as paraffin, fines, and the like on the components downhole, e.g., such that the flapper does not fully close or does not fully open, it is known to replace the TRSV by retrieving the safety valve assembly to surface by pulling the entire tubing string from the well and replacing the safety valve assembly with a new assembly, and then rerunning the safety valve and the tubing string back into the well. Because of the length of time and expense required for such a procedure, it is known to run a replacement safety valve downhole within the TRSV. These replacement safety valves are run downhole via a wireline, and thus often referred to as wireline insertable safety valves (“WISV”). Before inserting the WISV into the TRSV assembly, however, two operations are performed. First, the TRSV is locked in its open position (i.e., the flapper must be maintained in the open position); and second, fluid communication is established from the existing control fluid line to the interior of the TRSV, thus providing control fluid (e.g. hydraulic fluid) to the WISV. Lockout tools perform the former function; communication tools perform the latter. When it is desired to lock the safety valve assembly in its open position, the lockout tool is lowered through the tubing string and into the TRSV. The lockout tool is then actuated to lock the valve mechanism (e.g. the flapper) of the TRSV in the open position.
Before inserting the WISV, communication is established between the hydraulic chamber of the TRSV and the internal diameter of the TRSV. The communication tool is utilized to provide fluid communication between the inner diameter of the TRSV and the hydraulic chamber, so that the hydraulic control line from surface can be utilized to operate the WISV. Once communication has been established with the hydraulic chamber, the WISV is run downhole. The WISV may resemble a miniature version of the TRSV assembly. The WISV is placed within the inner diameter of the TRSV assembly. The WISV includes an upper seal above the communication flow passageway and a lower seal below the flapper and at a bottom sub, and the control line to the TRSV is used to actuate the valve mechanism of the WISV. More specifically, the upper and lower seals allow control fluid from the control line to communicate with the hydraulic chamber and piston of the WISV in order to actuate the valve of the WISV between the open and closed positions. Once the WISV is in place, the wireline is removed and the tubing string placed on production.
The art would be receptive to more robust downhole systems incorporating TRSV and WISV, and improved methods for operating downhole in varying and extreme conditions experienced by such downhole systems.